am I starting af?

Last night i had brown discharge with a little bit of red towards the end of the night so I put a tampon in before I slept. When I woke up and took the tampon out there was lots of brown, almost black blood and some very red blood too. My period has been late for 28 days so it's a relief if this is af starting. However, my periods don't usually start like this. Is this normal?